Reverberation unit having vibration-isolating suspension



3 Sheets-Sheet l I N VENTORI dlllz w mm Cofa%e,% L

BY 71/ M Na HMM mm SW i WNW w Nov. 15, 1966 w. c. LAUBE, JR

REVERBERATION UNIT HAVING VIBRATION-ISOLATING SUSPENSION Filed April 26,1962 NOV. 15, 1966 w, c, LAUBE, JR 3,286,204

REVERBERATION UNIT HAVING VIBRATION-ISOLATING SUSPENSION Filed April 26,1962 5 Sheets-Sheet 2 INV NTOR:

Nov. 15, 1966 w. c. LAUBE, JR

REVERBERATION UNIT HAVING VIBRATIONISOLATING SUSPENSION 5 Sheets-Sheet 5Filed April 26, 1962 IN VEN TOR: Mm 0 XM,%/@

United States Patent O 7 Delaware Filed Apr. 26, 1962, Ser. No. 190,4444 Claims. (Cl. 333-30) This invention relates in general toreverberation units for use with musical instruments, such as electricalorgans, radios or phonograph-s, and more particularly relates to animproved andmore economical transmission spring and suspension systemfor a reverberation unit assembly.

Reverberation units generallyv comprise several coil springs which serveas transmission lines to convey signals in different time intervals toan output circuit for the. purpose of simulating the acoustical effectof an auditorium. In such a unit there must be provided a signalgenerating assembly'or driver comprising an input coil, at one end ofthe spring. The input coil responds to an input electrical signal forcontrolling a tiny magnet attached to the adjacent end of the respectivetransmission lines. This introduces a corresponding mechanical wave intothe transmission line which is sensed byv a signal receiving assembly orpickup atthe other end of. the line. The pickup assembly comprisesanother magnet and coil which respond to the transmitted mechanical waveby providing an. output electrical signal having a delayed intervaldependent on thelengthiofthe spring and the rateof wave transmission.This output signal is then applied through suitable amplifying devicesto an output transducer, such as a loud speaker, for the purpose ofsimulating the effect described above.

The usual reverberation unit incorporates springs of considerable lengthin. order to secure delay intervals of appreciable magnitude, and inorder to provide different time delay periods, the springs in therespective transmission lines are of differing unstretched length, Sinceone of the lines incorporates a long spring in order to provide longdelay intervals, it governs the overall dimension of the unit andtherefore all springs may be stretched to the same length but differ inthe number of turns and helix angle. In addition, the springs areextremely sensitive to external sources of vibration.

The latter problem while not too acute in certain circumstances becomesof extreme importance if the reverberation unit is mounted in a movableassembly such as an automobile or adjacent the bass speakers of an audiosystem. The problems then are to reduce the overall longitudinaldimension of the reverberation unit while also isolating, thereverberation unit springs from sources of external vibration.

To reduce the length of the springs, and therefore the reverberationunit, of course, resultsin shorter delay periods. In order to overcomethis problem it would ordinarily be necessary to provide the springswith a larger helix diameter, but this in turn militates against thevassage of the higher frequencies through the spring. Here it wasrealized that while at least two transmission lines are necessary toprovide adequate reverberation, at the higher frequencies only onetransmission line is necessary since such frequencies are largely lostin an auditorium in any event and therefore would not be detected by theear. This is also true in a reverberation unit if the difference incut-off frequency between the two transmission lines is not too great.In addition, since the signal velocity and therefore the delay isdependent on the helix angle of the springs, the overall length of thesprings may be reduced by providing a minimum stretch in the springs3,286,204 Patented Nov. 15, 1966 just sufficient to enable the adjacentturns to clear each other.

In view of this the present invention utilizes two springs of differinghelix diameter for the purpose of introducing different time delayperiods with the smaller helix diameter spring operating into the higherfrequency range. All springs are wound to the same length and number; ofturns, with their turns in compression. In mounting the springs in thereverberation unit, they are stretched by the-smallest incrementnecessary to insure that the adjacent turns clear, so that the helixangle is heldsmall while the number of turns that may be provided isquite large. The signal velocity is therefore reduced sufficiently toenable a delay of a character similar to that achieved by springs oftwice the length in theprevious units, while at the same time sufficienthigh frequency signals are passed by the smaller diameter spring tosimulate theeffect of an auditorium.

The isolation of the springs from external vibration presents severalproblems in that the most necessary isolation should occur in the. rangeofbetween. and

4000 cycles through which the unit is intended to function mosteffectively and the cutoff frequency-of-the iso-' to findlothe'r meansfor reducing thetransmitted external lower frequency vibrations. Theunit can of course be shock mounted on springs,- which is a commonexpedient; however, this may be self defeating and expensive since themounting springs also have optimum frequencies which they will pass andsince the unit must be capable of being held in any of severalpositions. As the system is orthogonal, a unilaterally-compliant springwould normallybe-requiredfor each direction from which vibrations maybetransmitted.

In such a spring supported arrangement the static sag of the unitcorresponds to a resonant frequency at which harmfulvibrations arepassed most effectively. Below this resonant frequency the stiffness ofthe spring system is to great to provide isolation while above this'fre-' quency the mass of the unit controls. It is therefore necessaryto provide a mounting inwhich the static sag' The, light springs may beself resonant at-a high frequency but this frequency is one at which themass of the unit controls.

The compliant springsare generally incapable'of any stable stress exceptunder tension, but stable equilibrium will occur at the juncture betweena plurality of compliant helical springs provided the springs aremounted along non-parallel axes so that they have lateral as well asaxial compliance. Such a mounting system can easily be provided byconsidering the reverberation unit as being at the juncture of thesprings and suspending the unit from the mounting by means of coiledsprings which each have an axis normal to a respective plane of atetrahedron.

It is therefore an object of the present invention to provide animproved reverberation unit.

It is another object of the present invention to provide an improvedarrangement of the transmission l nes of a reverberation unit to, permitshortening the lines.

It is still another object of the present invention to provide animproved compliant supporting arrangement for a reverberation unit forthe purpose of isolating the unit from external vibrations.

Other objects together with the features of the present invention willbecome apparent on examination of the following specification, claimsand drawings, wherein:

FIG. 1 is an elevational view of the reverberation unit assembly;

FIG. '11: is an end view of the assembly shown in l with certain detailsomitted;

FIG. 2 is a' sectional view taken along the line 22 in FIG. 1;

FIG. 3 is asectional view taken along the line 33 in FIG. 2;

FIG. 4 is a sectional view taken along the line 44 in FIG. 3;'

FIG. 5 is a sectional view taken along the line 55 in 20. The channelmember 12' comprises opposite longitudinal side walls'22 and a back'wall23 therebetween.

Each wall is provided with apertures adjacent the pickup and driverassemblies for receiving respective coiled springs 24'24c. The springs24-24c' serve to suspend the reverberation unit from a suitable,mounting channel 25 for isolating the unit10 from extraneous vibrations.

The springs 24-24c are all wound so that they. are in. compression, andwhen assembled between channel meme ber 12' and the mounting channel 25they are stretched so that their turns are spaced apart forpreventingthe transmission of high frequencies and for permitting axialcompliance in both directions. It will be noted from FIG. la that thesprings are all stretched due to the spacing between the connections atchannel 12 and the connections at the mounting channel 25, while thestretch of springs 24a and 24b is also dependent on the mass.

of the unit 10. The mass of the unit 10 therefore results in a so-calledsag which is dependent on the spring constants and the mass of theiunit.The greater the sag, the lower the resonant frequency which will betransmitted. The springs 24-240 are therefore light so that the sag isof such nature that the resonant frequency will be below 30 cycles, forexample. It 'will also be noted that the unit 10 will be supported inthe same manner regardless of whether the mounting channel 25 isupright, as shown, or inverted, and that the. sag will be nearly thesame.

The springs being light will of course resonate at a high frequency andself resonance could be induced therein. The mass of the unit 10,however, is such that it will not respond to such high frequencies.

In addition, the arrangement of the four springs 24- 240 providesisolation for vibrations originating in substantially all directionssince the unit is in effect mounted at a juncture of the springs whichdo not have parallel axes and are laterally as well as axiallycompliant. Thus reference to FIGS. 1, 1a and 2 shows the relativedisposition ofthe spring axes between the channel 12 and the mountingchannel 25 is each normal to a different plane paralleling a tetrahedronso that any'force transmitted by one spring to the channel will interactat a transverse angle to the axis of each of the other springs andthereby damp the force out. The unit 10 at the juncture of thesprings'therefo re remains in a condition of substantial equilibrium.

The driver and pickup units 18 and 20 are substantial- 1y identicallyconstructed and dimensioned. Each in cludes an integrally formed case 26having a pair of spaced apart depending L-shaped lugs 27 that extendthrough the back wall 23 as best seen in FIGS. 4 and 5 and projecttowards each other. A shoulder 28 on each lug limits the downwardmovement of the case. A leaf spring 30 is inserted between therespective lugs 27 along the lower side of wall 23 to seat therespective cases 26 in position. An angle stop 32 on the leaf springengages the edge of wall 23 as best seen in FIGS. 2 and 3, while adetent '33 engages an aperture in wall 23 to control the position ofspring 30 and prevents its shifting. In addition, a ground strip 36 isinserted between the shoulders 28 and the top of wall 23 and is heldfirmly engaged against the wall 23 when clip 30 is inserted.

Each case 26 comprises a generally rectangular main body 3 8 having sidefaces 40, a front face 42, a back face 44, a top face 46, and a bottomface 48 from which the lugs 27 depend.' A groove 50 in both the top andbottom faces extends back from the front face 42 towards the rear of thebody 38 and a sloping stop element 52 having .a vertical rear wall 53 islocated in each groove as best seen in FIGS. 4 and 5.

The .body 38 is provided with a deep substantially rec-tan gularlyshaped recess 54 in its front face 42. The recess 54 has side walls 55intersected by vertical stop walls 56. In the posterior portion of therecess 54, as seen in FIGS. 3 and 5, the vertical walls converge and .anarrow aperture 58 connects the recess 54 to the back [face 44 of thebody. The aperture 58 is adapted to receive a connector strip 60 whichextends through the recess. 54 for the purpose of enabling electricalconnections to be extended to a coil 62. The coil 62 comprises part of acoil and pole piece assembly 64 adapted to be received in the recess 54and in a pair of horizontal slots 66.

A horizontal slot 66 connects each side of the recess 54 withthe sidefaces 40 of the body 38 for a predetermined distance from the front face42. Each slot 66 is'define-d by flat upper and lower wall portions 68from the front face 42 to a position intermediate the slot ends and thenby arcuate top and bottom wall portions 70 which terminate at a stopwall 72 as best seen in ,FIG. 6. A narrow horizontal passageway 74connects each slot 66 through the wall 72 to the back face 44 where therespective passageways terminate in a circular' opening recess 76.Narrow recesses 77 aligned crosswise to the passageways 74 extendinwardly from the opening 76.

The' coil and pole piece assemblies 64, as best seen in FIGS. 7 and 8,each comprise a bobbin 78 on which the coil 62 is wound in aconventional manner. The

bobbin 78 has a rectangular passageway 80 therein and generallyrectangular spool heads 82. A pair of pole pieces 84 are each adapted tobe engaged on a respective spool head 82 and each has a core portion 86for engagement in the passageway 80.

The pole pieces .84 each comprise an elongate web 88 of magneticmaterial and the respective core portions 86 depend therefrom adjacentthe transverse axisof the web and to one side thereof. An L-shapedflange- 90 is provided at opposite ends of each pole piece and eachflange has an arm 92 extending in opposing direc-' tions. The coreportions 86 are inserted through spool heads 82 into opposite ends ofpassageway 80 and in abutting relationship. The webs 88 are thussupported so that the arms 92 on one pole piece .are in a more closelyspaced relationship to an .arm on the other pole piece than the polepiece webs. This reduces the area of flux leakage to that of arms 92since only these areas are in close proximity to each other.

The spacing between respective arms 92 defines the gaps 93 of identicalmagnetic circuits and a tiny cylindrical magnet 94 at the end of eachtransmission line is 10- cated in each of the gaps. The magnets 94 eachhave an axial dimension substantially the same as the transversedimension of the associated arms 92. It will be noted that the magnets94 intersect the confined main flux path in the limited area traversedby arms 92 so that maximum signal efiiciency is achieved. In additionthe construction enables the gaps for the magnets at each end of bothtransmission lines to be effectively defined by a single pair of polepieces and these are all interchangeable.

It will be noted that each of the spool heads 82 is provided with a boss98 along one end and that a recess 100 is provided in one end of eachboss. Each recess 100 is adapted to receive respective arms 102 of theconnector stnip 60. The connector strip 60 is a flat elongate insulatingplate 103 upon which is afiixed a pair of thin conductive layers 104 towhich respective ieads 106 of the coil are extended at 'lugs 107. Thestrip 60 has top and bottom stop portions i108 which abut the back ofrecess 54 when the coil and pole .piece assembly 64 is inserted inrecess 54. A tab portion 110 onconnector strip 60 extends throughaperture 58 for the purpose of extending external electrical leads 11-2to the coil. The leads 112 are positioned by a tab 114 that is stakedonto wall 23.

The magents 94 each have a central aperture in which a stepped tube 116is inserted and cemented thereto. The stepped tube 1.16 has a portionwhich is cemented to and crimped about a respective straight end 118 ofa coil spring 120 or 122. The springs 120 and 122 each form a part of arespective transmission iline 14 or 16. Each transmission line comprisestwo sp nings 120 or 122 -respectively joined in the center of the line'by an eyelet, for example, and connected at opposite ends to the magnets94. The springs 120 or 122 are joined so that their windings are ofopposite direction for the purpose of suppressing undesired vibrationalmodes.

It will be noted that although the springs of each transmission line areof identical length that the springs 122 of the transmission line 16have a helix diameter of, for example, .198" and the springs 120 of line14 have a smaller helix diameter of .178", for example. Thus the springsof each line are wound to the same length of approximately 1.8" witheach having approximately 139 turns, these being in compressiverelationship so that adjacent turns are normally touching. Whenassembled to the driver and pickup assemblies, the springs are stretchedto just separate the turns and the smaller diameter line 14 will ofcourse transmit higher frequencies than the larger diameter line 16 withtheir cutoff frequency differing by a value depending on their helixdiameter difference. A stretch of only 1.5" per transmission line sothat the total length approaches only 8" with a separation of between.003" and .007" between adjacent turns has been found quite feasible. Inthe range where the frequency transmitted by line 16 begins to fall offsubstantially, little acoustical effect is lost since in that range thesingle line 14 contributes suflicient reverberation effect. Since thehelix angle is held small, a delay of appreciable magnitude is alsosecured within the short total length.

Due to the step in the tube 116, a shoulder is formed which serves as astop for a flattened end of a support wire 124 inserted partiallytherethrough as best seen in FIG. 6. The support wire 124 is extendedthrough a rubber damping disc 126 and its end is fastened along onediameter of an anchor disc 128 which serves as a bayonet connection aswill be explained. Thus each transmission line 14 and 16 is a selfcontained subassembly comprising a pair of coiled springs 120 or 122joined in the center of the line and having at each end a magnet 94,support wire 124, damping disc 126 and anchor disc 128.

To assemble the reverberation unit, a coil and pole piece assembly 64 isinserted in recess 54 in each case 26 with the tab 110 projecting fromthe rear of the case. The ground strip 36 which has an elongate leg 132extends towards the front face 42 and this is bent over and inserted 6.between the lower pole piece and associated spool head before theassembly 64 is inserted in recess 54. Each case 26 is mounted on thechannel 12 and-held thereto by the leaf springs 30 either before orafter the assembly 64 is inserted in recess 54, but in either event thewalls 55 and 56 in recess 54 serve to control the position of theassembly 64. The transmission lines 14 and 16 are assembled to thedriverand pickup assemblies 18 and 20 by inserting the anchor disc 128at one end of each transmission line through the passageway 7.4, and onpassing therethrough and being aligned with circular opening 76, each isgiven a slight rotational movement and a slight pull thereon enables theanchor disc 128 to be seated in the recesses 77 to form a bayonetconnection. is then no longer aligned with the passageway 74, it cannotbe pulled back through it so that one end of each transmission line isheld in position. The disc 128 at the other end-of each transmissionline is then inserted through a passageway 74 in either the driver orpickup means as the case may be in the same fashion.

The distance between the two ends of passageways 74 is calculated tojust stretch the springs so that their turns areseparated by anidenticalamount with the turns having a low helix angle to insure theproper propagation of the transmitted waves while at the same timethe-total spring length is held short. Thus, by the positioning of thecases 26 the correct spacing between the .turns can be easily achieved.The magnets-94 then lie in the gaps 93 formed between a respective pairof arms 92 of the pole pieces.

In order to properly position and secure the pole pieces with respect tothe magnets 94 while securing the coil and pole piece assembly 64 and inorder to maintain the damping discs 126 properly positioned, a springclip 134 is used to complete the positioning of the assembly. The clip134 is generally U-shaped with the ends of the side legs 135 having ringshaped slotted right angle arms 136 thereon. In addition, a pair ofwings 137 are provided at the end of each leg 135 and in the same plane,but projecting back therefrom at a transverse angle.

The back leg 138 of the clip 134 is provided with respective upwardlyand downwardly projecting tines 139 and L-shaped arms 140. Each arm 140has a locking bend 142 at the end thereof.

The clips 134 is assembled to the case 26 by inserting the side legs 135together with wing 137 in the recess 54 while arms 140 engage grooves50. The slots in ring shaped arms 136 permit the arms to engage over thewire 126 between the magnets 94 and damping discs 126. As the clip 134is pressed back, the arms 136 move the damping discs 126 through slots66 between the arcuate wall portions 70 and 72 to properly seat thesame. At the same time the wings 137 press the webs 84 of the polepieces against the respective upper and lower walls of recess 54 to sizethe gap 93 therebetween. Simultaneously the Walls 56 serve as stops forthe arms 90 so that the pole pieces are positioned properly with respectto the magnets 94.

The tines 139 serve to apply pressure against the coil and pole pieceassembly 64 and when the locking bend 140 on the clip passes over thevertical wall 53 of the stop 52, the assembly is securely held inposition.

A rectangular resilient shielding element 142 is slipped over the frontof the driver unit case 26 preferably before the transmission lines 14and 16 are assembled thereto. The element 142 has a set of cars 143which engage around a tab 144 protruding from the sides of each case sothat the element 142 is properly seated and supported. The element 142additionally seats the leg 132 of the ground strip 36 against the bottomface 48 of the case so that it is in no danger of entranglement.

There has been described one embodiment of my invention, and since thisembodiment is capable of many adaptations and modifications, there isappended hereto a series of claims for accurately setting forth thelimitations of the invention.

Since the anchor disc 128 I claim:

1. A suspension system for a vibration sensitive reverberation unitutilizing electroacoustic transducers, for the purpose of vibrationallyisolating the reverberation unit comprising, a subframe for saidreverberation unit, said subframe in end elevation providing attachmentpoints arranged in substantially a rectangular pattern with diagonallyopposite corners of the rectangle at the same end of the subfrarne, aseparate mounting frame, four coil tension springs supporting saidreverberation unit, one of said springs being connected at one end toone of said attachment points and to said mounting frame, another ofsaid springs being connected to the diagonally opposite attachment pointat the same end of the subframe and to the mounting frame, said springsin tension being angled relative tothe subframe to produce a centeringcomponent on said subframe end relative to said mounting frame and alsoto produce a rotary component on said subframe in one direction, theother pair of springs being connected to beration unit utilizingelectroacoustic transducers for the.

purpose of vibrationally isolating the reverberation unit comprising, amounting frame, four substantially identical coil springs supportingsaid reverberation unit, said springs being, in tension and connected atone end to said reverberation unit at spaced points and to the mountingframe at their other ends at spaced points, and the angularity of thesprings being such that the axis of each spring is normal to a differentface of a tetrahedron.

3. In a suspension system for a vibration sensitive reverberation unitutilizing electroacoustic transducers, the combination recited in claim1 in which the tension springs are angled such that no two have parallelaxes.

4. In a suspension system for a vibration sensitive reverberation unitutilizing electroacoustic transducers, the combination recited in claim1 in which said springs are each normal to a different tetrahedral face.

References Cited by the Examiner UNITED STATES PATENTS 1,016,077 1/1912Lumley 21754 2,211,205 8/ 1940 Hammond 333-71 2,230,836 2/1941 Hammond33371 2,480,131 8/1949 Hammond 841.15 2,768,235 10/1956 Knoblauch 179-12,799,778 7/ 1957 Stephenson 21754 2,967,447 1/ 1961 Hanert 84-1.263,092,792 6/1963 Daniel 33330 3,106,610 10/1963 Young 179-1 FOREIGNPATENTS 677,326 '8/ 1952 Great Britain. 730,729 5/ 1955 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

C. BARAFF, Assistant Examiner.

2. A SUSPENSION SYSTEM FOR A VIBRATION SENSITIVE REVERBERATION UNITUTILIZING ELECTROACOUSTIC TRANSDUCERS FOR THE PURPOSE OF VIBRATIONALLYISOLATING THE REVERBERATION UNIT COMPRISING, A MOUNTING FRAME, FORSUBSTANTIALLY IDENTICAL COIL SPRINGS SUPPORTING SAID REVERBERATION UNIT,SAID SPRINGS BEING IN TENSION AND CONNECTD AT ONE END TO SAIDREVERBERATION UNIT AT SPACED POINTS AND TO THE MOUNTING FRAME AT THEIROTHER ENDS AT SPACED POINTS, AND THE ANGULARITY OF THE SPRINGS BEINGSUCH THAT THE AXIS OF EACH SPRING IS NORMAL TO A DIFFERENT FACE OF ATETRAHEDRON.